The invention relates to a circular knitting machine for the production of knit goods having combed-in fibers with a preselected fiber density comprising a rotatable needle cylinder having needles with needles hooks, a means for driving the needle cylinder during knitting cyles, and a card which has means for feeding fibers, a comb-in zone through which the needles pass for contactless reception of fibers, and a teasing cylinder rotating at high speed which picks up the fibers from the feeding means and yields them to the comb-in zone.
In methods and circular knitting machines of this kind (U.S. Pat. Nos. 4,458,506 and 4,546,622) the fibers, in contrast to conventional methods and circular knitting machines (U.S. Pat. No. 3,709.002) are combed contactlessly into the needle hooks, the term "contactlessly" meaning that the needle hooks do not pass through teasing hooks. The transfer of the fibers to the comb-in zone is performed as in circular knitting machines with conventional combs under conditions synchronous with the rotation of the needle cylinder. The term, "synchronous conditions", is to be understood to mean that, at any constant rotatory speed of the needle cylinder, the fibers are always delivered to the comb-in zone at a preselected, constant amount of fibers per unit time, so as to produce goods having a preselected, constant fiber density. On the other hand, the amount of fiber fed to the comb-in zone changes synchronously in the case of changes in the needle cylinder rotatory speed, in order that, in the event of reductions or increases in the needle cylinder rotatory speed, correspondingly less or more fibers will be delivered to the comb-in zone, thereby assuring that the preselected fiber density will be achieved at any rotatory speed of the needle cylinder, i.e., especially during the execution of start and stop cycles. If the feed of fiber to the teasing cylinder is by means of feed rolls, for example, "synchronous conditions" means that the feed rolls and the needle cylinder are driven from a single, main drive through gears, belts, rollers or the like, so that the ratio of their rotatory speeds is the same at all rotatory speeds of the needle cylinder, and that, independently thereof, the teasing cylinder is driven always at the same high rotatory speed at all needle cylinder speeds.
Experiments on such circular knitting machines with contactless fiber feed have surprisingly shown that, during those phases in which the needle cylinder is subjected to abrupt changes of rotatory speed, such as is the case especially during the start and stop cycles and during "tip" operation, undesirable deviations from the preselected fiber density can result, which lead to thick and thin areas in the finished knit goods. "Thick and thin areas" in this connection refers to those points in the finished goods at which the fiber density is lower or higher than the preselected fiber density. The length of the thick and thin areas appears to be dependent upon a number of factors, such as the length of time for which the needle cylinder is stopped, the fiber length or the titer of the fibers.
The invention is therefore addressed to the problem of improving the circular knitting machine of the kind defined such that thick and thin areas will be largely avoided. In particular, those thick and thin areas are to be avoided such as are observed after the needle cylinder has been stopped.
The knitting machine of this invention is characterized by first protective means which can be actuated for preventing fibers from being fed to the needles, by second protective means which can be actuated for preventing fibers from being removed from the needles, and by actuating means for actuating said first and second protective means such that the preselected fiber density of the knit fabric is substantially maintained constant also when the needle cylinder is stopped and again started between successive knitting cycles.
The invention brings with it the advantage that, when the needle cylinder is stopped, those fiber tufts are retained which have already been inserted into needles, but remain with the needles in the comb-in zone for the duration of the stoppage. Since these fiber tufts are in opened needle hooks, their density might become accidentally either increased or decreased, and this is effectively prevented by the protective device of the invention. In accordance with the invention, therefore, retention of the fiber tufts means that, during the stoppages of the needle cylinder, no additional fibers are fed to and no fibers are removed from the needles in the comb-in zone. Thus it is possible to prevent a number of the thick and thin areas which can be observed when the protective device is lacking.
Additional advantageous features of the invention will be found in th subordinate claims.
The invention will now be further explained in conjunction with the appended drawing of a preferred embodiment.